AWR中的DB Time和CPU time

    在AWR中的等待事件中的CPU time总是弄不清，不过今天总算弄清楚了。

   官方文档Performance Tuning Guide/5 Automatic Performance Statistics：

     This statistics represents the total time spent in database calls and is a indicator of the total instance workload. It is calculated by aggregating the CPU and wait times of all sessions not waiting on idle wait events (non-idle user sessions).

    DB Time=  CPU time + 非空闲wait time;

    在等待TOP5的等待事件中，CPU time不是等待事件，而是实际消耗CPU的时间。%Total call Time  是这么计算的， 如在等待事件中的CPU time  91.9% = 6,527/(118.40*60)。

     还有一点可以总结：通过这两个时间，我们就可以知道数据库到底是负载高还是等待事件严重。

	Snap Id	Snap Time	Sessions	Cursors/Session
Begin Snap:	20684	06-2月 -13 14:00:45	377	13.6
End Snap:	20688	06-2月 -13 18:00:35	354	15.0
Elapsed:		239.83 (mins)
DB Time:		118.40 (mins)

Event	Waits	Time(s)	Avg Wait(ms)	% Total Call Time	Wait Class
CPU time		6,527		91.9
db file sequential read	332,367	324	1	4.6	User I/O
log file parallel write	32,029	286	9	4.0	System I/O
log file sync	31,044	283	9	4.0	Commit
db file parallel write	11,633	71	6	1.0	System I/O